Infrared discharge lamp having conical anode heated by bombardment with electrons emitted by filamentary cathode



Jan. 14, 1964 B. o. LANGE 3,118,081 INFRARED DISCHARGE LAMP HAVING CONICAL ANODE HEATED BY BOMBARDMENT WITH ELECTRONS EMITTED BY FILAMENTARY CATHODE Filed Jan. 30, 1961 United States Patent Q ,amin G. Lange, Mountain View, Calif., assignor to Lockheed Aircraft Cor oration, Burbank, Calif.

.lan. 3t), 1% Ser. No. 85,699 4 Claims. (till. 313-347) The present invention relates to a black body radiation source and more particularly to a black body radiation source capable of obtaining extremely high temperatures and stabilizing within a relatively short period of time.

It is well known in the art that heating of hollow cones provides an efiective black body radiation source. Various methods which have been used to heat hollow cones include an open flame, passing current through the cone, and passing current through a filament embedded in ceramic material contiguous to the cone. All of these methods have had the serious limitation of being unable to obtain temperatures greater than about 1000 degrees centigrade. In addition, the open flame method is cumbersome and difiicult to control. Heating by passing current through a cone requires large currents and results in nonuniform current density and corresponding nonuniform temperature. Passing current through a ceramic embedded filament is ineflicient. In addition to the above, in order for these prior methods to obtain temperatures of about 1060 degrees centigrade it is necessary that considerable insulation be disposed about the cone and heater. Since the insulation absorbs and dissipates heat slowly, it takes considerable time to raise or lower the cone temperature to establish different operating points. Frequently the time required between different points is of the order of several hours.

Tie present invention obviates the disadvantages of these prior methods by disposing a hollow cone in a vacuum and bombarding the cone with electrons which intensely heat the cone upon transmission of their kinetic energy to the cone surface upon collision therewith. By this method it is possible to heat the cone to about 2,500 degrees Centigrade, obtain stable rapid temperature changes (by requiring minimum insulation), and provide an extremely uniform temperature over the entire cone surface.

Accordingly, an object of the present invention is to provide an economical, highly effective black body radiation source.

Another object is to provide a high temperature radiation or visible source which is uniform in intensity over its area when viewed from the detector.

Another object is to provide a black body radiation source that is able to obtain a temperature of about 2,500 degrees Centigrade.

A further object is to provide a black body radiation source that is able to provide a stable temperature change over a relatively short period of time.

Still another object is to provide a black body infrared radiation device having a hollow cone which is heated by the absorbed kinetic energy of electrons colliding therewith.

The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing in which:

FIGURE 1 is a detailed illustration of the present invention.

FIGURE 2 is a diagrammatic illustration of FIGURE 1 and shows the electrical connections thereof.

Like numerals designate like elements throughout the figures of the drawing.

In FIGURE 1 is illustrated an enclosed envelope 11 made of glass or other material capable of withstanding high temperatures. Envelope 11 comprises a large cylindrical portion 12 and a small cylindrical portion 13. In the outer end of small cylindrical portion 13 is mounted a small window 14 which is rigidly sealed in place by fusion, cement or other suitable fastening methods. Window 1 may be made of sapphire or other light transmitting material capable of transmitting light in the infrared and visible light spectrum of from about 5 to about .2 micron or any other particular range of interest. I11 those instances when window 14 has a considerable different coefficient of expansion than that of the envelope material, the small cylindrical portion may be made from a plurality of fused cylindrical rings having progressively varying coefiicients of expansion. In this manner high stress concentrations are prevented from being developed and the envelope will not be destroyed at high temperatures. Disposed within large cylindrical portion 12 of envelope i3 is hollow cone 15 made of a thin sheet of tungsten or similar material. Connected to the apex of cone 15 are rigid lead wires 16 for supporting the cone as well as providing an electrical connection to a positive potential source. The other end of lead wires 16 are welded to plate 17 which is made of electrical conducting material. Rigid rods 18, made of electrical conducting material, are welded to plate 17 and pass through and extend beyond sealing nodules 19 at the end of large cylindrical portion 12.

In order to provide electron bombardment of cone 5, filament wire 21 is spaced from and surrounds the exterior surface thereof. One end of filament wire 21 is connected to rod 23 and the other end is connected to circular support plate 25. Mounted on the face of support plate 25 are cylindrical radiation shields 27 which have progressively decreasing diameters and are concentrically mounted thereby providing an insulating space therebetween. Each radiation shield is provided with an aperture 29 to permit the transmission of radiation from the interior surface of cone 15 through window l4. Welded to support plate 25 are rods 31 which pass through and extend beyond sealing nodules 33'. Plate member 35 is mounted by rods 37 which extend through and beyond sealing nodules 38 and welded to the surface of plate member 35 is rod 23 which is attached to filament wire 15 thereby providing an electrical connection between the filament and the extended portion of rods 37.

In FIGURE 2 is schematically illustrated the electrical connections of the present invention. Potential source 39, which may have an ouput of from about 10 to about 20 volts, is connected to filament 21 with the negative side thereof connected to shields 2.7. Potential source 41, which may have an output of from about 0 to about 900 volts, has the positive side thereof connected to cone 15. In operation, current is passed through the filament which results in the emission of electrons. Since the cone is maintained at a positive potential with relation to the emitted electrons by potential source 41, these emitted electrons are attracted to the surface thereof and upon contact, their kinetic energy is converted into heat energy resulting in high cone temperature. Since shield 27 is at a negative potential, the emitted electrons are repelled therefrom and directed towards the cone. Shield 27 also reflects heat energy radiated from the cone surface thereby making it possible to obtain higher cone temperatures and prevents envelope 11 from becoming excessively heated. It has been found that electron bombardment of the cone surface is uniform which results in the temperature of the entire cone surface being highly uniform. In addition, since the surrounding shield is of relatively small mass, it is possible to readily shift from one to another operating temperature in the order of a few minutes. Temperature control is readily obtained by changing the current through the filament and/or changing the potential applied to the cone.

It is to be understood in connection with this invention that the embodiment shown is only exemplary, and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

What is claimed is:

1. A device for emitting light energy comprising a hollow cone, a filament disposed in spaced relation from said cone, a potential source operatively connected to said filament for passing current therethrough, a poten tial source operatively connected to said cone, said second-mentioned potential source being positive in relation to said first-mentioned potential source, said cone and filament disposed in an evacuated envelope, a light transmitting window disposed in said envelope for transmitting the light emitted from the interior surface of said hollow cone, whereby the electrons emitted from said filament upon the passage of current therethrough are accelerated towards said cone by said positive potential applied to said cone and upon contact with said cone release their kinetic energy resulting in heating of said cone.

2. A device for emitting light energy in the infrared energy region of the light spectrum comprising a hollow cone having a thin wall, a filament spaced from and surrounding the exterior surface of said hollow cone, a shield surrounding said cone and filament, means passing current through said filament, means applying a potential to said cone, the potential of said second-mentioned means being positive in relation to the potential of said first-mentioned means, means applying a potential to said shield, the potential of said last-mentioned means being negative in relation to the potentials of said first and second-mentioned means, said cone, filament and shield being disposed in an evacuated envelope, a light transmitting window disposed in said envelope for transmitting the light emitted from the interior surface of said hollow cone, whereby the electrons emitted from said filament upon the passage of current therethrough are repelled from said shield and accelerated toward said cone and upon contact with said cone cause heating thereof by the conversion of the kinetic energy of said electrons into heat energy.

3. A device for emitting light energy in the infrared energy region of the light spectrum comprising a hollow cone having a thin wall, a filament spaced from and sur rounding the exterior surface of said hollow cone, a shield surrounding said cone and filament and having an aperture at one end, means passing current through said filament, means applying a potential to said cone, the potential of said second-mentioned means being positive in relation to the potential of said first-mentioned means, means applying a potential to said shield, the potential of said last-mentioned means being negative in relation to the potentials of said first and second-mentioned means, said cone filament and shield being disposed in an evacuated envelope, an infrared light transmitting member disposed in said envelope for transmitting the light emitted from the interior surface of said cone and through said aperture whereby the electrons emitted from said filament upon the passage of current therethrough are repelled from said shield and accelerated toward said cone and upon contact With said cone are capable of heating said cone to about 2,500 degrees centigrade by the conversion of the kinetic energy of said electrons into heat energy.

4. A device for emitting light energy in the infrared energy region of the light spectrum comprising a hollow cone having a thin wall, a filament spaced from and surrounding the exterior surface of said hollow cone, a shield surrounding said cone and filament and having an aperture at one end, means passing current through said filament, means applying a potential to said cone, the potential of said second-mentioned means being positive in relation to the potential of said first-mentioned means, means applying a potential to said shield, the potential of said last-mentioned means being negative in relation to the potentials of said first and second-mentioned means, said cone, filament and shield being disposed in an evacuated envelope, having a longitudinally extending member, an infrared light transmitting member disposed at the end of said longitudinally extending member wherein said aperture of said shield, said longitudinally extending member and said light transmitting member are about axially aligned with respect to the axis of said cone such that the light emitted from the interior surface of said cone is transmitted through said aperture, said longitudinally extending member, and said light transmitting member, whereby the electrons emitted from said filament upon the passage of current therethrough are repelled from said shield and accelerated toward said cone and upon contact with said cone are capable of heating said cone to about 2,500 degrees centigrade by the conversion of kinetic energy of said electrons into heat energy.

References Cited in the file of this patent UNITED STATES PATENTS 2,140,348 Clark Dec. 13, 1938 2,189,786 Fischer Feb. 13, 1940 2,284,389 Hansen May 26, 1942 2,410,822 Kenyon Nov. 12, 1946 2,888,591 Schmidt May 26, 1959 2,912,616 Marchese 'Nov. 10, 1959 

1. A DEVICE FOR EMITTING LIGHT ENERGY COMPRISING A HOLLOW CONE, A FILAMENT DISPOSED IN SPACED RELATION FROM SAID CONE, A POTENTIAL SOURCE OPERATIVELY CONNECTED TO SAID FILAMENT FOR PASSING CURRENT THERETHROUGH, A POTENTIAL SOURCE OPERATIVELY CONNECTED TO SAID CONE, SAID SECOND-MENTIONED POTENTIAL SOURCE BEING POSITIVE IN RELATION TO SAID FIRST-MENTIONED POTENTIAL SOURCE, SAID CONE AND FILAMENT DISPOSED IN AN EVACUATED ENVELOPE, A LIGHT TRANSMITTING WINDOW DISPOSED IN SAID ENVELOPE FOR TRANSMITTING THE LIGHT EMITTED FROM THE INTERIOR SURFACE OF SAID HOLLOW CONE, WHEREBY THE ELECTRONS EMITTED FROM SAID FILAMENT UPON THE PASSAGE OF CURRENT THERETHROUGH ARE ACCELERATED TOWARDS SAID CONE BY SAID POSITIVE POTENTIAL APPLIED TO SAID CONE AND UPON CONTACT WITH SAID CONE RELEASE THEIR KINETIC ENERGY RESULTING IN HEATING OF SAID CONE. 